OpenSourceParking.com is a domain parking service that helps Free Software and Open Source. Domain parking provides a place-holder web page for an undeveloped domain name.
According to netcraft:
An open source initiative to reverse gains for Microsoft web server software appears to be using edited server headers to try and improve the showing of the Apache web server. Sites using the Open Source Parking service report that they are running on Apache, but appear to actually be hosted on lighttpd. Both Apache and lighttpd are open source web servers, but Apache leads in the Netcraft survey with a 59 percent market share, while lighttpd is a newcomer with just 1.2% share.
This may be implemented for security reasons. There is no need to create a fake open source parking spoofing headers to benefit Apache. Both are open source and robust web servers. Personally this site runs using Lighttpd because of limited resources. Generally I use lighttpd to push static content (images, cached HTML pages and other files) and use Apache for real work :).